1. Field of the Invention
The present invention relates to the use of an aqueous solution in scrubbing sulfur oxide from the gases exhausted from a combustion process. More particularly, the invention relates to the use of an aqueous solution of high reserve alkalinity in plural zones, each of the zones controlled to different pH values, to react with sulfur dioxide (SO.sub.2) and remove it from combustion gases.
2. Description of the Prior Art
A long-standing problem is the air pollution by sulfur oxides in gases discharged from the combustion of sulfur-containing fuels. There are removal systems which use an aqueous solution having materials which will react with the sulfur oxides upon contact.
The most commonly used contact materials may be limestone and dolomite. These materials have been added to the furnace in which combustion takes place. An aqueous slurry has also been formed of these materials to contact and remove, or scrub, SO.sub.2 from the combustion gases. However, there are several handling problems with these materials because they are insoluble. Additionally, the chemistry of their system is hard to control in order to avoid precipitates. And precipitates of this material can physically obstruct the vessels and piping to result in shutdowns. Additionally, the physical access of limestone and dolomite may be a factor in their use.
Evidently a soluble chemical will make it easier to control the pH of the reactions with SO.sub.2. Further, the pH of the reactions may be more readily maintained at different values in separate zones to maximize the efficiency of the final reaction while minimizing the quantity of the chemical used to react with the SO.sub.2.